We have a state-of-the-art mass spectrometry with highly trained technical staff. Several methodologies described in this proposal have been developed within our laboratory. The laboratory hs continuously making technical advances in terms of state-of-the-art equipment and development of novel and innovative techniques. Currently, the facility is supported in part by an NIH grants through the GCRC and Obesity Nutrition Research Center and the center of the support comes from various Foundation grants which the Principal Investigator has obtained through the Mayo Development Department. All of the technological developments initiated by the current technical staff will continue but the current commitments do not allow them to undertake any additional work. Most of the analysis involved in this study are highly time consuming and the time necessary from two additional technicians is essential for the time completion of all analyses. This Core also will provide support to the investigators in interpreting stable isotope data and bringing them up-to-date on new developments in the field.